Grain size analysis of the latest Quaternary Kordofan Sand of Central Sudan: Depositional environment and mode of transportation

Abstract

Grain size analysis is a powerful tool for determining the depositional environment. Grain size analysis for 48 samples from four sections along a 280 km long, nearly north–south-trending transect, has been conducted in the mainly Holocene Kordofan Sand in the Kordofan Region of Central Sudan. In these sections, this part of the Kordofan Sand comprises three pedosedimentary sequences. The lower sequence (∼13–10 kyr) has been pedogenized during the African Humid Period and ends up farther West with lacustrine or palustrine carbonates. The middle sequence (∼6–3 kyr) is represented by sand with low degree of pedogenesis and corresponds to the African Humid Period. The upper sequence was deposited after a hiatus lasting from ∼3.3 to 1.1 ka BP, and constitutes the present-day surficial deposits, showing little or no pedogenesis. Spatial grain size distribution and mode of transport show a southward fining trend, indicating that the sandy sediments were transported from north to south. This interpretation is supported by the results of mean grain size – sorting, and sorting – skewness interrelations, which provided a linear relationship. Vertical variation in grain size distribution in the studied sections shows variable energy over time in the north and constant, low energy in the south. The dominance of saltation as a transport mode confirms that the studied sediments were deposited in aeolian environment. The low sorting degree, the presence of coarse grains, and the still active transverse dunes and barchans in the North, indicate that the Late Pleistocene part of the Kordofan Sandstone is submitted to reworking until now. Consequently, the mainly Holocene sand sequences were fed both by distal, fine-grained Saharan material and by proximal, coarser-grained sand proceeding from the Late Pleistocene aeolian dunes.